From above T1, proprioceptive primary axons enter the spinal cord and ascend ipsilaterally until reaching the accessory cuneate nucleus , where they synapse. The secondary axons pass into the cerebellum via the inferior cerebellar peduncle where again, these axons synapse on cerebellar deep nuclei. This tract is known as the cuneocerebellar tract. Motor information travels from the brain down the spinal cord via descending spinal cord tracts.
Then, the lower motor neuron conducts the nerve signal to the spinal root where efferent nerve fibers carry the motor signal toward the target muscle. The descending tracts are composed of white matter. There are several descending tracts serving different functions. The corticospinal tracts lateral and anterior are responsible for coordinated limb movements. A congenital disorder is diastematomyelia in which part of the spinal cord is split usually at the level of the upper lumbar vertebrae.
Sometimes the split can be along the length of the spinal cord. Spinal cord injuries can be caused by trauma to the spinal column stretching, bruising, applying pressure, severing, laceration, etc. The vertebral bones or intervertebral disks can shatter, causing the spinal cord to be punctured by a sharp fragment of bone. Usually, victims of spinal cord injuries will suffer loss of feeling in certain parts of their body. In milder cases, a victim might only suffer loss of hand or foot function.
More severe injuries may result in paraplegia , tetraplegia also known as quadriplegia , or full body paralysis below the site of injury to the spinal cord. Damage to upper motor neuron axons in the spinal cord results in a characteristic pattern of ipsilateral deficits. These include hyperreflexia , hypertonia and muscle weakness.
Lower motor neuronal damage results in its own characteristic pattern of deficits. Rather than an entire side of deficits, there is a pattern relating to the myotome affected by the damage.
Additionally, lower motor neurons are characterized by muscle weakness, hypotonia , hyporeflexia and muscle atrophy. Spinal shock and neurogenic shock can occur from a spinal injury. Spinal shock is usually temporary, lasting only for 24—48 hours, and is a temporary absence of sensory and motor functions. Neurogenic shock lasts for weeks and can lead to a loss of muscle tone due to disuse of the muscles below the injured site. The two areas of the spinal cord most commonly injured are the cervical spine C1—C7 and the lumbar spine L1—L5.
The notation C1, C7, L1, L5 refer to the location of a specific vertebra in either the cervical, thoracic, or lumbar region of the spine. Spinal cord injury can also be non-traumatic and caused by disease transverse myelitis , polio , spina bifida , Friedreich's ataxia , spinal cord tumor , spinal stenosis etc. In the U. Real or suspected spinal cord injuries need immediate immobilisation including that of the head. Scans will be needed to assess the injury. A steroid, methylprednisolone , can be of help as can physical therapy and possibly antioxidants. Regeneration is facilitated by maintaining electric transmission in neural elements.
The spinal cord ends at the level of vertebrae L1—L2, while the subarachnoid space —the compartment that contains cerebrospinal fluid — extends down to the lower border of S2.
Spinal tumours can occur in the spinal cord and these can be either inside intradural or outside extradural the dura mater. A portion of the spinal cord, showing its right lateral surface. The dura is opened and arranged to show the nerve roots. The spinal cord with dura cut open, showing the exits of the spinal nerves. From Wikipedia, the free encyclopedia. This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources.
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Nervous System Organization
Main article: Spinal cord injuries. The spinal cord showing how the anterior and posterior roots join in the spinal nerves. Projections of the spinal cord into the nerves red motor, blue sensory. Cross-section of adult mouse spinal cord: astrocytes red and neurons green. Cross section of adult rat spinal cord stained using Cajal method. Sagittal section of pig vertebrae showing a section of the spinal cord. Spinal cord. Spinal membranes and nerve roots. Deep dissection. Posterior view. Brachial plexus.
Inferior view. This article uses anatomical terminology; for an overview, see anatomical terminology. Human biology and health 1st ed. Englewood Cliffs, N. Frontiers in Neurology. Exploring Psychology. Worth Publishers. Fundamental neuroscience 4th ed. Retrieved December 27, Life Map Discovery Compendium. Retrieved 12 Dec Stem Cell Development Compendium.
Retrieved 2 Dec Mc Graw Hill. Annual Review of Neuroscience. Essential Clinical Anatomy, Third Edition. April Journal of Thoracic and Cardiovascular Surgery. Anatomy and Physiology, 5th Ed. McGraw-Hill Professional Publishing. Human systems and organs. Fibrous joint Cartilaginous joint Synovial joint. Muscle Tendon Diaphragm. Skin Subcutaneous tissue Breast Mammary gland. Myeloid Myeloid immune system Lymphoid Lymphoid immune system.
Genitourinary system Kidney Ureter Bladder Urethra. General anatomy : systems and organs , regional anatomy , planes and lines , superficial axial anatomy , superficial anatomy of limbs. Nervous system. Sensory nerve Motor nerve Cranial nerve Spinal nerve. These include hormone release, movement of food through the stomach and intestines, and the sensations from and muscular control to all internal organs.
This diagram illustrates these pathways and the level of the spinal cord projecting to each organ. Although spinal cord injury causes complex damage, a surprising amount of the basic circuitry to control movement and process information can remain intact. This is because the spinal cord is arranged in layers of circuitry. Many of the connections and neuronal cell bodies forming this circuitry above and below the site of injury survive the trauma.
An important question to research scientists is, how much do these surviving neurons "know? Research points to a multiplicity of possible interventions to promote recovery from a spinal injury. Some would be delivered immediately following the injury; others are less time-specific and involve rebuilding and reconnecting the injured cord.
Clearly, both approaches are important: limiting degeneration will enhance the probability of greater recovery, while stimulating regeneration will build upon the remaining system to restore lost connectivity and perhaps to prevent further degeneration. This is not a comprehensive list of all possible interventions. Grantees undertaking projects under government sponsorship are encouraged to express freely their findings and conclusions.
Points of view or opinions do not, therefore, necessarily represent official Administration for Community Living policy. Reeve Foundation. How does the central nervous system differ from other systems of the body? How does the central nervous system protect itself from injury? Cells of the central nervous system Synapses and neurotransmission What causes paralysis?
The information pathways Voluntary and involuntary movement How the spinal cord and muscles work together How the spinal cord and internal organs work together What happens following a spinal cord injury? Intervention strategies. What is the central nervous system? Cells of the central nervous system Neurons connect with one another to send and receive messages in the brain and spinal cord. Oligodendrocytes are glial cells that produce a fatty substance called myelin which wraps around axons in layers.
Axon fibers insulated by myelin can carry electrical messages also called action potentials at a speed of meters per second, while fibers without myelin can only carry messages at a speed of one meter per second. Synapses and neurotransmission Messages are passed from neuron to neuron through synapses, small gaps between the cells, with the help of chemicals called neurotransmitters.
Edited by John N. Wood
What causes paralysis? The information pathways Specialized neurons carry messages from the skin, muscles, joints, and internal organs to the spinal cord about pain, temperature, touch, vibration, and proprioception. Voluntary and involuntary movement Over one million axons travel through the spinal cord, including the longest axons in the central nervous system. How the spinal cord and muscles work together The spinal cord is divided into five sections: the cervical, thoracic, lumbar, sacral, and coccygeal regions.
How the spinal cord and internal organs work together In addition to the control of voluntary movement, the central nervous system contains the sympathetic and parasympathetic pathways that control the "fight or flight" response to danger and regulation of bodily functions. What happens following a spinal cord injury? A common set of biological events take place following spinal cord injury: Cells from the immune system migrate to the injury site, causing additional damage to some neurons and death to others that survived the initial trauma.
The death of oligodendrocytes causes axons to lose their myelination, which greatly impairs the conduction of action potential, messages, or renders the remaining connections useless. The neuronal information highway is further disrupted because many axons are severed, cutting off the lines of communication between the brain and muscles and between the body's sensory systems and the brain. Within several weeks of the initial injury, the area of tissue damage has been cleared away by microglia, and a fluid-filled cavity surrounded by a glial scar is left behind.
Molecules that inhibit regrowth of severed axons are now expressed at this site. The cavitation is called a syrinx, which acts as a barrier to the reconnection of the two sides of the damaged spinal cord. Intervention strategies Research points to a multiplicity of possible interventions to promote recovery from a spinal injury. Treatments immediately following an accident: Limiting initial degeneration Recent research has shown that there are at least three different mechanisms of cell death at play in neuronal and oligodendrocyte loss after injury: necrosis, excitotoxicity, and apoptosis.
Treating inflammation Soon after injury, the spinal cord swells and proteins from the immune system invade the injured zone. This swelling and inflammation may foster secondary damage to the cord after the initial injury. So it is important to treat the inflammatory response as quickly as possible. Labs pursuing this approach include the Schwab Lab. Extending from C8 to L3, it receives viscerosensory information and contains preganglionic sympathetic neurons, which form the lateral horn.
A large proportion of its cells are root cells which send axons into the ventral spinal roots via the white rami to reach the sympathetic tract as preganglionic fibers. Similarly, cell columns in the intermediolateral nucleus located at the S2 to S4 levels contains preganglionic parasympathetic neurons Figure 3. Lower motor neuron nuclei are located in the ventral horn of the spinal cord.
The a motor neurons are the final common pathway of the motor system, and they innervate the visceral and skeletal muscles.
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The distribution of cells and fibers within the gray matter of the spinal cord exhibits a pattern of lamination. The cellular pattern of each lamina is composed of various sizes or shapes of neurons cytoarchitecture which led Rexed to propose a new classification based on 10 layers laminae. This classification is useful since it is related more accurately to function than the previous classification scheme which was based on major nuclear groups Figure 3. Laminae I to IV, in general, are concerned with exteroceptive sensation and comprise the dorsal horn, whereas laminae V and VI are concerned primarily with proprioceptive sensations.
Lamina VII is equivalent to the intermediate zone and acts as a relay between muscle spindle to midbrain and cerebellum, and laminae VIII-IX comprise the ventral horn and contain mainly motor neurons. The axons of these neurons innervate mainly skeletal muscle. Lamina X surrounds the central canal and contains neuroglia. Rexed lamina I — Consists of a thin layer of cells that cap the tip of the dorsal horn with small dendrites and a complex array of nonmyelinated axons. Cells in lamina I respond mainly to noxious and thermal stimuli. Lamina I cell axons join the contralateral spinothalamic tract; this layer corresponds to nucleus posteromarginalis.
Rexed lamina II — Composed of tightly packed interneurons. This layer corresponds to the substantia gelatinosa and responds to noxious stimuli while others respond to non-noxious stimuli. The majority of neurons in Rexed lamina II axons receive information from sensory dorsal root ganglion cells as well as descending dorsolateral fasciculus DLF fibers. High concentrations of substance P and opiate receptors have been identified in Rexed lamina II.
The lamina is believed to be important for the modulation of sensory input, with the effect of determining which pattern of incoming information will produce sensations that will be interpreted by the brain as being painful. Rexed lamina III — Composed of variable cell size, axons of these neurons bifurcate several times and form a dense plexus. Rexed lamina IV — The thickest of the first four laminae. In addition, dendrites of neurons in lamina IV radiate to lamina II, and respond to stimuli such as light touch. The ill-defined nucleus proprius is located in the head of this layer.
Some of the cells project to the thalamus via the contralateral and ipsilateral spinothalamic tract. Rexed lamina V — Composed neurons with their dendrites in lamina II. This lamina covers a broad zone extending across the neck of the dorsal horn and is divided into medial and lateral parts. Many of the Rexed lamina V cells project to the brain stem and the thalamus via the contralateral and ipsilateral spinothalamic tract. Moreover, descending corticospinal and rubrospinal fibers synapse upon its cells.
Rexed lamina VI — Is a broad layer which is best developed in the cervical and lumbar enlargements. Lamina VI divides also into medial and lateral parts. Group Ia afferent axons from muscle spindles terminate in the medial part at the C8 to L3 segmental levels and are the source of the ipsilateral spinocerebellar pathways. Many of the small neurons are interneurons participating in spinal reflexes, while descending brainstem pathways project to the lateral zone of Rexed layer VI.
Rexed lamina VII — This lamina occupies a large heterogeneous region. This region is also known as the zona intermedia or intermediolateral nucleus. Its shape and boundaries vary along the length of the cord. Lamina VII neurons receive information from Rexed lamina II to VI as well as visceral afferent fibers, and they serve as an intermediary relay in transmission of visceral motor neurons impulses.
The dorsal nucleus of Clarke forms a prominent round oval cell column from C8 to L3. The large cells give rise to uncrossed nerve fibers of the dorsal spinocerebellar tract DSCT. Cells in the lateral horn of the cord in segments T1 and L3 give rise to preganglionic sympathetic fibers to innervate postganglionic cells located in the sympathetic ganglia outside the cord.
Lateral horn neurons at segments S2 to S4 give rise to preganglionic neurons of the sacral parasympathetic fibers to innervate postganglionic cells located in peripheral ganglia. Rexed lamina VIII — Includes an area at the base of the ventral horn, but its shape differs at various cord levels. In the cord enlargements, the lamina occupies only the medial part of the ventral horn, where descending vestibulospinal and reticulospinal fibers terminate.
The neurons of lamina VIII modulate motor activity, most probably via g motor neurons which innervate the intrafusal muscle fibers. Its size and shape differ at various cord levels. Rexed lamina X — Neurons in Rexed lamina X surround the central canal and occupy the commissural lateral area of the gray commissure, which also contains decussating axons.
In summary, laminae I-IV are concerned with exteroceptive sensations, whereas laminae V and VI are concerned primarily with proprioceptive sensation and act as a relay between the periphery to the midbrain and the cerebellum. All visceral motor neurons are located in lamina VII and innervate neurons in autonomic ganglia. Surrounding the gray matter is white matter containing myelinated and unmyelinated nerve fibers.
These fibers conduct information up ascending or down descending the cord. The white matter is divided into the dorsal or posterior column or funiculus , lateral column and ventral or anterior column Figure 3. The anterior white commissure resides in the center of the spinal cord, and it contains crossing nerve fibers that belong to the spinothalamic tracts, spinocerebellar tracts, and anterior corticospinal tracts. Three general nerve fiber types can be distinguished in the spinal cord white matter: 1 long ascending nerve fibers originally from the column cells, which make synaptic connections to neurons in various brainstem nuclei, cerebellum and dorsal thalamus, 2 long descending nerve fibers originating from the cerebral cortex and various brainstem nuclei to synapse within the different Rexed layers in the spinal cord gray matter, and 3 shorter nerve fibers interconnecting various spinal cord levels such as the fibers responsible for the coordination of flexor reflexes.
Ascending tracts are found in all columns whereas descending tracts are found only in the lateral and the anterior columns. Four different terms are often used to describe bundles of axons such as those found in the white matter: funiculus, fasciculus, tract, and pathway. Funiculus is a morphological term to describe a large group of nerve fibers which are located in a given area e. Within a funiculus, groups of fibers from diverse origins, which share common features, are sometimes arranged in smaller bundles of axons called fasciculus, e. Fasciculus is primarily a morphological term whereas tracts and pathways are also terms applied to nerve fiber bundles which have a functional connotation.
A tract is a group of nerve fibers which usually has the same origin, destination, and course and also has similar functions. The tract name is derived from their origin and their termination i. A pathway usually refers to the entire neuronal circuit responsible for a specific function, and it includes all the nuclei and tracts which are associated with that function.
For example, the spinothalamic pathway includes the cell bodies of origin in the dorsal root ganglia , their axons as they project through the dorsal roots, synapses in the spinal cord, and projections of second and third order neurons across the white commissure, which ascend to the thalamus in the spinothalamic tracts. Ascending tracts Figure 3. The ascending tracts transmit sensory information from the sensory receptors to higher levels of the CNS.
The ascending gracile and cuneate fasciculi occupying the dorsal column, and sometimes are named the dorsal funiculus. These fibers carry information related to tactile, two point discrimination of simultaneously applied pressure, vibration, position, and movement sense and conscious proprioception. In the lateral column funiculus , the neospinothalamic tract or lateral spinothalamic tract is located more anteriorly and laterally, and carries pain, temperature and crude touch information from somatic and visceral structures.
Nearby laterally, the dorsal and ventral spinocerebellar tracts carry unconscious proprioception information from muscles and joints of the lower extremity to the cerebellum. In the ventral column funiculus there are four prominent tracts: 1 the paleospinothalamic tract or anterior spinothalamic tract is located which carry pain, temperature, and information associated with touch to the brain stem nuclei and to the diencephalon, 2 the spinoolivary tract carries information from Golgi tendon organs to the cerebellum, 3 the spinoreticular tract, and 4 the spinotectal tract.
Structure and function of the brain
Intersegmental nerve fibers traveling for several segments 2 to 4 and are located as a thin layer around the gray matter is known as fasciculus proprius, spinospinal or archispinothalamic tract. It carries pain information to the brain stem and diencephalon. Descending tracts Figure 3. The descending tracts originate from different cortical areas and from brain stem nuclei. The descending pathway carry information associated with maintenance of motor activities such as posture, balance, muscle tone, and visceral and somatic reflex activity. These include the lateral corticospinal tract and the rubrospinal tracts located in the lateral column funiculus.
These tracts carry information associated with voluntary movement. Other tracts such as the reticulospinal vestibulospinal and the anterior corticospinal tract mediate balance and postural movements Figure 3. Lissauer's tract, which is wedged between the dorsal horn and the surface of the spinal cord carry the descending fibers of the dorsolateral funiculus DFL , which regulate incoming pain sensation at the spinal level, and intersegmental fibers.
Additional details about ascending and descending tracts are described in the next few chapters. Information from the skin, skeletal muscle and joints is relayed to the spinal cord by sensory cells located in the dorsal root ganglia. The dorsal root fibers are the axons originated from the primary sensory dorsal root ganglion cells.